1. Field of the Invention
The present invention relates to a magnetic recording/reproduction apparatus used as a hard disk drive and, more particularly, to a magnetic recording/reproduction apparatus using perpendicular magnetization, and a perpendicular magnetic recording medium for use in the apparatus.
2. Description of the Related Art
Conventionally, the easy axis of magnetization of a magnetic recording layer is paralleled to a magnetic recording medium. In a perpendicular magnetic recording system, this easy axis of magnetization is perpendicular to the magnetic recording medium. This decreases the demagnetizing field near a magnetization transition region as a boundary between recording bits. Therefore, as the linear recording density increases, the medium becomes magnetostatically stable, and the thermal decay resistance increases. This makes the system suited to increasing the areal recording density. Also, When this high-magnetic-permeability soft magnetic layer is formed, a so-called double layered perpendicular recording medium having a perpendicular magnetic recording layer on the soft magnetic layer is formed. In this double-layered perpendicular recording medium, the soft magnetic layer performs part of the function of a magnetic head for magnetizing the perpendicular magnetic recording layer. That is, a recording magnetic field supplied from the recording head to magnetize the perpendicular magnetic recording layer is moved in the horizontal direction and returned to the magnetic head by this soft magnetic layer. In this manner, the soft magnetic layer can increase the recording capability and the recording/reproduction efficiency.
In this double-layered perpendicular recording medium, however, the soft magnetic backing layer is formed below a perpendicular magnetic recording layer. Accordingly, the material of an underlayer used to reduce the size of grains in the recording layer is considerably limited. In addition, to obtain high recording capability by using the medium in combination with a single-pole head, the space between the soft magnetic backing layer and the recording layer must be narrowed. To form an underlayer between them, the thickness of this underlayer is desirably as thin as possible.
Various proposals have been made to reduce the size of the magnetic grains in a magnetic recording layer and reduce the medium noise of this perpendicular magnetic recording medium. Unfortunately, none of these proposals is satisfactory.
As an example of such proposals, Jpn. Pat. Appln. KOKAI Publication No. 6-103550 discloses a three-layered soft magnetic backing layer including a first soft magnetic layer, a nonmagnetic layer, and a second soft magnetic layer having a thickness of 0.3 μm or less.
Also, a soft magnetic backing layer having a stacked structure made up of a first soft magnetic layer, oxide layer, second soft magnetic layer, and oxide layer is disclosed in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 10-228620.